The present invention relates to a process for producing metal-containing layers, in particular metal-containing diffusion barriers, contact layers and/or antireflection layers, in particular for use in CMOS circuits or DRAM memory modules and also in so-called xe2x80x9cembedded DRAMxe2x80x9d modules.
Integrated circuits, in particular CMOS circuits or DRAM memory modules, are fabricated by a multiplicity of process steps. The costs for fabricating these circuits are in this case determined by the process complexity and the physical processing time. Highly complex modules frequently require several hundred individual process steps and multiple days for completing the process cycle of the product.
Some of the process steps have to be used for the contact-making of doped regions in the semiconductor substrate or for the contact-making of two conductive layers. In modern DRAM and logic generations, contacts between silicon and tungsten are frequently used for the contact-making of doped regions in the semiconductor substrate. However, it is possible to use other metals such as, for example, aluminum. In order to avoid undesirable tungsten-silicon reactions (xe2x80x9cencroachmentxe2x80x9d, xe2x80x9cwormholesxe2x80x9d) or aluminum-silicon reactions (xe2x80x9cspikingxe2x80x9d), metal-containing layers, for example Ti/TiN layers, are frequently employed as contact or barrier layers between silicon and tungsten or silicon and aluminum.
Ti/TiN or TiSi2 contact layers are also frequently used in the case of contacts between two conductive layers. By way of example, a TiN layer over an Al layer reduces the natural oxidation of the Al layer and, consequently, leads to low-impedance contacts or serves as an antireflection layer. Likewise, the provision of a TiSi2 layer on a polysilicon gate is a measure for considerably increasing the power of MOS transistors.
Owing to the multiplicity of possible applications, metal layers, in particular titanium layers, are also the subject of a series of investigations. Thus, by way of example, the publications xe2x80x9cNitridal-on of Polycrysealline Titanium as Studied by in situ Angle-resolved X-ray Photoelectron Spectroscopyxe2x80x9d, A. Ermolieff et al. in xe2x80x9cSurface and interface Analysisxe2x80x9d Vol. 11, Pages 563-568 (1988), xe2x80x9cTungsten Contacts for a 256M DRAM Process Upsing A Thermally Formed TiN Diffusion Barrierxe2x80x9d, J. Gambino et al., 1996 VMIC Conference 1996 ISMICxe2x80x94106/96/0180i(c), Jun. 18-20, and xe2x80x9cInfluence Of The Spuotering Method Of TiN/Ti Films On The Resistance Of High Aspect Ratio Contact Holesxe2x80x9d, R. Kanamura et al., 1996 VMIC Conference 1996 ISMICxe2x80x94106/96/0554(c), Jun. 18-20 deal with properties and applications of titanium-containing layers.
The above-mentioned applications presuppose, however, particularly in the case of small structure widths, metal-containing layers of good Tuality, in order that the desired properties of the metal-containing layers can actually be obtained. In this case, effectively preventing contamination of the metal-containing layer or oxidation of the met al during the process cycle is a matter of particular importance. However, this cannot be guaranteed in the case of conventional processes for producing metal-containing layers, which leads to increased contact resistances, for example.
It is accordingly an object of the invention to provide a process for producing metal-containing layers which overcomes the above-mentioned disadvantages of the prior art methods of this general type.
In particular, an object of the present invention is to provide a process for producing metal-containing layers which largely prevents oxidation of the metal during the process.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing metal-containing layers including metal-containing diffusion barriers, contact layers, and antireflection layers on a semiconductor structure, which includes:
applying a metal layer having a predetermined thickness at an elevated temperature on a semiconductor structure; and
cooling the metal layer in a nitrogen-containing atmosphere resulting in a formation of a metal nitride layer.
The use of a nitrogen-containing atmosphere has the advantage, on the one hand, that the cooling time is shortened as a result of the faster heat dissipation compared with conventionally used inert gases such as argon. As a rule, this results in a distinctly increased plant throughput, which in turn has a positive effect on the fabrication costs. The cooling time can be reduced by about 40% by the use of a nitrogen-containing atmosphere.
On the other hand, otherwise unavoidable oxidation of the metal layer is considerably reduced by the metal nitride layer (passivation layer) that forms. The consequence of this is that less oxygen is incorporated in the metal layer, which enables smaller contact resistances and, ultimately, a smaller metal layer thickness as well. This in turn has a positive effect on the throughput that can be achieved. The technical possibility for using for example xe2x80x9cTi linersxe2x80x9d or the use of titanium for salicide processes can thus be extended technologically for further product generations.
The metal layer is preferably applied at a temperature of more than 100xc2x0 C., in particular more than 300xc2x0 C.
Furthermore, it is preferred if the metal layer is cooled to a temperature of less than 100xc2x0 C.
In accordance with a preferred embodiment, the metal layer is applied by a chemical vapor deposition (CVD) process or a physical vapor deposition (PVD) process, in particular a sputtering technique.
Furthermore, it is preferred if the metal used is titanium, tantalum, molybdenum or tungsten.
Preferably, a titanium layer is applied to a silicon surface.
In this case, it is particularly preferred if the titanium layer is subjected to a heat treatment after cooling in a nitrogen and hydrogen-containing atmosphere, with the result that the titanium reacts to form titanium silicide at the area of contact with the silicon.
The heat treatment should be carried out at a temperature of about 500 to 1000xc2x0 C., preferably 600 to 900xc2x0 C.
Furthermore, it is preferred for some applications if the titanium nitride layer is removed, preferably by wet-chemical processes, after the completion of the titanium-containing layer.
Furthermore, it is preferred if the application of the metal layer is carried out in a first chamber and the cooling of the metal layer is carried is carried out in a second chamber. The semiconductor structure is transported from the first chamber into the second chamber after the application of the metal layer, with the vacuum conditions being maintained. This effectively prevents nitridation of the metal source for the application of the metal layer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process for producing metal-containing layers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.